It isn't clear how they are chosen. Is there a lottery? A quota? Are there genetic markers that indicate who will be a better soldier?
Loyal families give up their children. Loyal to what? What would the price be of disloyalty? Death? Whose death? How many deaths?
They're trained from birth. How old are the troops? Who came before them, and where did they go?
Some people talk about mercy. Is it mercy to hold your child before they're taken away, raised to be a killer? Or to have them stolen when all you've known of their life is pain?